A mixture of fragmented DNA was electrophoresed in an agarose gel. After staining the gel with ethidium bromide, no DNA bands were observed. What could be the reason?

Explanation

To solve the question regarding why no DNA bands were observed after electrophoresis of fragmented DNA in an agarose gel, we can break down the potential reasons step by step:

### Step-by-Step Solution:

1. **Contamination of DNA Sample**:
- The DNA sample may have been contaminated with nucleases (exonucleases or endonucleases). These enzymes can degrade DNA, leading to complete degradation of the DNA fragments. If the DNA is degraded, there will be no intact DNA to visualize on the gel.

2. **Incorrect Electrode Orientation**:
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